How do you enable the subscribe button on Facebook? It's very simple. Just click the green button on the upper right of Facebook's Introducing the Subscribe Button page. That's it!
In response to Google+ and a long overdue response to Twitter, Facebook inevitably had to roll out a one-way follow feature. While Facebook was obviously built on engaging with your friends (or making a billion dollars, naturally), then uploading photos (and by uploading, I mean creeping on), the demand for content sharing and following influential people has continued to snowball. Now, Facebook Profiles can be treated similarly to Facebook Fan Pages in that you can simply follow others without them following you back.
Along with the Subscribe Button, Facebook rolled out features that easily allow people to decide who they share their posts with, whether it's Public, Friends, or a Custom Group, which is similar to Google Circles.
It will be very interesting to see how celebrities (this definitely includes tech celebrities who have been promoting this all day), athletes, journalists, and politicians embrace the Faecbook Subscribe Button. There is a fine line between what you want to share with the public as a whole (like you would with Twitter), and what is more private for your friends or custom groups. Also, Facebook doesn't have the best reputation for privacy so I'm sure many will be rather skeptical, especially at first.
If you visit somebody who is your Facebook friend and they have enabled the Facebook Subscribe Button, then it will show up as 'Subscribed' already. If you go to somebody's page who you want to follow and they have the button enabled, but aren't friends with on Facebook (such as the very intelligent Dharmesh Shah or some Facebooker named Mark Zuckerberg), just click the Facebook Subscribe Button in the upper right. If your not friends and they don't have the Subscribe button, then they haven't turned it on (share this with them!) or they're over.
What do you think about the Facebook Subscribe Button and how it will affect Google+ and Twitter? Also, who do you want to follow on Facebook?